Arthropods, such as mosquitoes, are often a nuisance to humans and other animals. Arthropods can also be vectors for diseases. Due to the nuisance and public health issues, humans strive to control arthropod populations near their environments. One way of controlling arthropods is by using pyrethroids.
Pyrethroids are axonic excitoxins which prevent the closure of the voltage-gated sodium channels in the axonal membranes of arthropods. The toxins work by paralyzing the organism.
While pyrethroids are effective arthropod adulticides, a major problem is that populations of arthropods are developing resistance to them. Pyrethroid resistance, caused either by specific detoxification enzymes or an altered target site mechanism (Jcdr-type mutations in the sodium channels), has been reported on most continents in the majority of medically important mosquito species. If resistance continues to develop and spread at the current rate, it may render such insecticides ineffective in their current form. Such a scenario would have potentially devastating consequences in public health terms, because there are as yet no obvious alternatives to many of the pyrethroids.
Resistance is a complex phenomenon arising from exposure to the same or a similar insecticide class over a period of multiple insect generations. Resistance develops due to extinction of susceptible individuals within the population and survival with subsequent reproduction of individuals who are inherently “immune” to the effects of the insecticide. Resistance can be due to multiple factors that include selection of target site mutations, detoxification enzymes and decreased cuticular penetration. Resistance may arise in naive populations that have been previously identified as insecticide susceptible or those that have been exposed to insecticides of another or similar class or mode of action. Cross resistance can occur and, in addition to physiological resistance, behavioral resistance mechanisms may also be present. The end result of resistance to current control measures is that available insecticides are often inadequate to provide the mortality rates necessary achieve sufficient levels of arthropod control at environmentally acceptable application rates. Because pyrethroid resistant insects pose a significant human health risk, there is a need in the art for a safe and effective arthropod insecticide.
One type of arthropod that is a major health concern is mosquitoes. The three major genera of mosquitoes which transmit diseases are Anopheles, Culex and Aedes. Therefore, there is a need to control mosquitoes to reduce disease transmission.
Insecticides can attack any stage of the insects' development. However, it is the mosquito in the adult stage that transmits viruses and parasites which cause disease. Control of larval stages is a first line of defense for suppression of mosquito populations, but without the capacity to control adult mosquitoes the ability to manage disease can be severely compromised in many settings.
In the past, the problem of insecticide resistance has been solved by rotating conventional insecticides of varying chemistries. However, resistance to multiple chemistries has developed in many settings, complicating this approach. Therefore, there is a need for a new approach to overcoming insecticidal resistance.
U.S. Pat. No. 6,306,415 is directed to methods of repelling flies by topically applying a composition containing a 1:1:1 ratio of octanoic acid, nonanoic acid and decanoic acid as the only active ingredients. U.S. Pat. No. 6,444,216 is directed to compositions and methods to repel insects containing a mixture of fatty acids as the only active ingredients. These patents do not discuss the possibility of using these compounds in combination with a pyrethroid.
McAllister, et al., Mode of Action for Natural Products Isolated from Essential Oils of Two Trees is Different From Available Mosquito Adulticides, J. Med. Entomol. 47(6): 1123-1126, discusses the possible utility of thymoquinone, nootkatone, and carvacrol for treating pyrethroid resistant strains of mosquitoes, but does not discuss the possibility of using these compounds in combination with pyrethroids.
The compositions of the prior art have failed to produce an environmentally safe adulticide that is effective on pyrethroid resistant and pyrethroid susceptible arthropods.